On the basis of the Institute of Electrical and Electronics Engineers (IEEE) 802.16e Standard (hereinafter, “WiMAX”: Worldwide Interoperability for Microwave Access), which is in the process of being standardized as a specification for a high-speed wireless network to realize a next-generation mobile communication system, communication device manufacturers and operators in various countries have been performing mutual connection tests and field trials to achieve commercialization, which is now realized.
For example, there are techniques for wirelessly transferring sound data by using wireless communication techniques intended for relatively short distance communications, such as Bluetooth (registered trademark). Examples of utilization modes of WiMAX described above include a mode using such a technique. For example, as depicted in FIG. 11, a wireless communication terminal (e.g., a portable terminal) using WiMAX wirelessly transfers data received from the wireless network side to another device (e.g., a headset) connected to the wireless communication terminal and positioned nearby. FIG. 11 is an exemplary configuration of a conventional wireless communication system.
Further, according to the wireless communication technique described above, if a plurality of communication terminals using mutually-different wireless communication methods perform communication while using mutually the same frequency band, there may be a situation where a radio wave interference occurs between the terminals and the communication performance may be degraded. To cope with this situation, for example, Japanese Laid-open Patent Publication No. 2002-300172 proposes a technique for inhibiting degradation of communication performance caused by a radio wave interference that occurs when a plurality of communication terminals using mutually-different wireless communication methods use mutually the same frequency band.
A wireless communication terminal that uses a plurality of wireless communication methods such as Bluetooth and WiMAX described above has a possibility of having a communication failure because of a radio wave interference occurring inside the terminal.
For example, the width of the available frequency range between the frequency bands “2.3 GHz and 2.5 GHz” used by WiMAX and the frequency band “2.4 gigahertz” used by Bluetooth is small. Accordingly, a wireless communication terminal configured so as to implement both WiMAX and Bluetooth has a possibility of having a radio wave interference on the inside of the terminal, WiMAX being a wireless communication method intended for external communications such as a communication with a wireless network and Bluetooth being a wireless communication method intended for an inter-device connection such as a communication with a device at a relatively short distance. As a result, a communication terminal that uses a plurality of wireless communication methods has a possibility of having a communication failure caused by a radio wave interference occurring inside the terminal.
To address the problem described above, techniques that can be used for avoiding such radio wave interferences occurring on the inside of wireless communication terminals have also been discussed. More specifically, as depicted in FIG. 12, a communication period width is defined while using WiMAX communication as a reference axis, so that a schedule is prepared in which sections during which WiMAX communication is performed and sections during which Bluetooth communication (“BT” in FIG. 12) is performed are time-shared. Based on the prepared schedule, the output of the frequency is stopped on the side corresponding to the wireless communication method by which no communication is performed, so that it is possible to avoid radio wave interferences that may occur on the inside of the terminal (called “co-existence function”). FIG. 12 is a scheduling example in which the sections during which WiMAX communication is performed and the sections during which Bluetooth communication is performed are time-shared.
According to the proposed technique described above, however, another problem as described below arises: It is reported that the maximum communication distance of WiMAX is tens of kilometers, whereas the maximum communication distance of Bluetooth is 100 meters. When communication is performed at the same time within a small area of a number of meters by a plurality of wireless communication terminals each of which is configured with a function of avoiding, on the inside thereof, internal interferences between the WiMAX communication and the Bluetooth communication, as depicted in FIG. 13, there is a possibility that a radio wave interference may occur between the WiMAX communication frequency and the Bluetooth communication frequency from the two different wireless communication terminals. FIG. 13 is a drawing for explaining the problem with the conventional example.